In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Conventionally, valve seats in, for example, combustion engines, have three surfaces arranged at angles to each other. FIG. 1 schematically illustrates the surfaces of a conventional valve seat 10 in a workpiece 12, with a top surface 14, a joining surface 16 and a stem surface 18. The top surface 14, joining surface 16 and stem surface 18 complement surfaces of a valve 20 to seat the valve 20 in the valve seat 10 during operation of the combustion engine. Alternative conventional valve seats can have from two to four or more surfaces.
The conventional method to form a valve seat with more than one surface uses a single effective material removal tool where one insert or blade cuts one of the three valve seat surfaces. The one insert or blade is typically an indexable insert and is arranged at the preset angle to the one valve seat surface to be machined and then the cutting operation is conducted. To machine the valve seat surfaces, a different insert edge, a different insert or even a different tool is brought into engagement with the workpiece to machine one of the remaining valve seat surfaces. This operation is repeated for each distinct valve seat surface. Using different tools, a single effective tool, and/or having to index or change indexable inserts can introduce angular errors into the part. However, tolerances on parts such as valve stem seating surfaces are very tight, and the conventional tools and methods of machining can introduce errors beyond those tolerated in specifications for such parts.